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workmg standard should be mamtamed at 015% mtnc aCId ThIS aCId should be added to the flask asneeded before the addItIon ofthe ahquot 7 Cahbratton 71 Transfer 0, 05, 10, 20, 50 and 10 ml ahquots of the workmg mercury solutIon (67) contammg0to 10ugofmercurytoasenesof300mlBODbottles AddenoughdIstIlled water to each bottle to make a total volume of 10 ml Add 5 ml of aqua regIa (6 1) and heat 2 mmutes m a water bath at 95°C Allow the sample to cool and add 50 ml dIstIlled water and 15 ml ofKMn04solutIOn (6 5) to each bottle and return to the water bath for 30 mmutes Cool and add 6 ml of sodIUm chlonde-hydroxylamme sulfate solutIOn (6 4) to reduce the excess permanganate Add 50 ml of dIstIlled water Treatmg each bottle mdividually, add 5 ml of stannous sulfate solutIOn (63) and ImmedIately attach the bottle to the aeratIOn apparatus At thIS pomt, the sample IS allowed to stand qUIetly WIthout manual agItatIOn The circulatmg pump, WhICh has prevIously been adjusted to rate of 1 hter per mmute, IS allowed to run contmuously The absorbance, as exhIbIted eIther on the spectrophotometer or the recorder, wIll mcrease and reach maXImum withm 30 seconds As soon as the recorder pen levels off, approxImately 1 mmute, open the bypass value and contmue the aeratIon unttl the absorbance returns to Its mmimum value (See Note 5) Close the bypass value, remove the fntted tubmg from the BOD bottle and contmue the aeratIOn Proceed With the standards and construct a standard curve by plottmg peak heIght versus mlCrogiams ofmercury NOTE 5: Because of the tOXIC nature of mercury vapor precautIOn must be taken to avoId Its mhaiatton Therefore, a bypass has been mcluded m the system to eIther vent the mercury vapor mto an exhaust hood or pass the vapor through some absorbmg medIa, such as a) equal volumes of0 1N KMn04 and 10% H2S04 b) 025% IOdme m a 3% KI SolutIon A specIally treated charcoal that wIll absorb mercury vapor IS also avatlable from BarnebeyandCheney,E 8thAve,andNorthCassIdySt,Columbus,OhIO43219, Cat #580-13 or #580-22 8 Procedure 8 1 82 WeIgh tnphcate 0 2 g portIOns ofdry sample and place m bottom ofa BOD bottle Add 5 ml of disttlied water and 5 ml of aqua regIa (6 1) Heat 2 mmutes m a water bath at 95°C Cool, add 50 ml disttlied water and 15 ml potassIUm permanganate solutIOn (65) to each sample bottle MIX thoroughly and place m the water bath for 30 mmutes at 95°C Cool and add 6 ml of sodIUm chlonde-hydroxylamme sulfate (64) to reduce the excess permanganate Add 55 ml of disttlied water Treatmg each bottle mdividually, add 5 m1 of stannous sulfate (63) and ImmedIately attach the bottle to the aeratIOn apparatus Contmue as descnbed under (7 1) An alternate dIgestIOn procedure employmg an autoclave may also be used In thIS method 5 ml ofconc H2S04and 2 ml ofconc HN03 are added to the 0 2 g ofsample 5 ml of saturated KMn04 SolutIon IS added and the bottle covered WIth a pIece of alummum fOil The samples are autoclaved at 121°C and 15 lbs for 15 mmutes Cool, make up to a volume of 100 ml WIth disttlied water and add 6 ml of sodIUm chlonde- 2455-3PDF Image | Methods for Chemical Analysis of Water and Wastes
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